Patent GB-650146-A (GB)
Title: Improvements in or relating to circuit-arrangements comprising at least one switch for the control of at least one conductive lead
IPC: H01J43/02
Filed: 1948-04-16
Abstract: 650,146. Two-way transmission; automatic exchange switches. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. April 16, 1948, No. 10638. Convention date, April 21, 1947. [Class 40 (iv)] [Also in Groups XL (a) and XL (c)] In a circuit arrangement for rendering at least one lead conductive or non-conductive two portions of the (or each) lead are each connected to one of a pair of secondary-emission collecting electrodes situated in a dischargetube, the path between the two electrodes of a pair being rendered conductive when electrons from the cathode of the tube impinge on the electrodes. As shown in Fig. 1, the sections 1a, 1b and 2a, 2b of the two leads 1, 2 (which may be a two-wire telephone line) are connected to the secondary-emission electrodes 5, 6 and 5a, 6a, respectively, included in a discharge tube (not shown) comprising a cathode 7 and grids 8, 9. The electrodes 5, 6, 5a, 6a are connected via equal resistors 10, 11, 10a, 11a to a tapping on battery 12, the negative pole of which is connected to the cathode 7, and with suitable voltages fed to 8, 9, electrons from the cathode strike 5, 6, 5a, 6a. If, therefore, an alternating voltage, e.g. a speech signal, is applied across 1a, 2a the potentials of the left-hand electrodes 5, 5a change, one, say that of 5, increasing and the other decreasing. Consequently, secondary electrons will flow from 6 to 5 and from 5a to 6a and a connection between the sections 1a and 1b, and 2a and 2b is established. In order to avoid distortion of the voltage to be transmitted additional grids 15a, 15b are provided and are connected to the positive pole of battery 12, the position and potential of these grids being so chosen that in the absence of incoming signals the secondary electron current flow to each grid is equal to the total electron current flow to the associated pair of electrodes. Under these conditions the secondary-emission current 5-6 is nil. To render the leads 1, 2 non-conducting a sufficiently negative potential is connected to grids 8 and/or 9. In the embodiment of Fig. 3 arrangements are provided for rendering a selected one of a plurality of leads conductive. A pair of secondary-emission electrodes, e.g. 16a, 16b is provided for each such lead and grids such as 15a, 15b of Fig. 1 are provided (not shown in Fig. 3). The deflecting plate 21 is kept at a constant potential and with zero voltage fed to plate 20 the cathode-ray beam 19 strikes a collecting electrode 22. To establish a connection between a pair of lead sections, e.g. 23a, 23b the beam is deflected so as to strike the associated pair of electrodes by applying a suitable voltage to plate 20. This voltage is applied at point 25 and thence through delay network 33 to plate 20, and in parallel to a differentiating network 27, 28 which produces a voltage pulse when the potential at 25 changes. This pulse is fed to a circuit 30 which produces a negative voltage pulse which is supplied to the control electrode 32 to suppress the beam during deflection. A blanking pulse is similarly produced when the potential at 25 is reduced to zero. The provision of a plate-shaped electrode in front of the secondary-emission electrodes with apertures opposite each pair is suggested (Fig. 5, not shown), the beam being focused on this electrode to ensure that on passing through one of the apertures it strikes both secondary-emission electrodes of a pair.